Power transmission unit for vehicle

ABSTRACT

A power transmission unit for a vehicle is provided. In the power transmission unit, a continuously variable transmission to alter a speed ratio continuously is disposed between an input shaft to which a torque of a prime mover is inputted and an output shaft rotated by the torque transmitted from the input shaft. A first gear train that transmits the torque to propel the vehicle in the forward direction is arranged parallel to a second gear train that transmits the torque to propelling the vehicle backwardly. The power transmission unit is comprised of: a first clutch device that selectively allows a torque transmitting route from the input shaft to the output shaft via the first gear train to transmit the torque therethrough; a dog clutch that switches the torque transmitting route from the input shaft to the output shaft between a continuously variable speed change route in which the torque is transmitted through the continuously variable transmission and a reverse route in which the torque is transmitted through the second gear train; and a second clutch device that connects and disconnects both of the continuously variable speed change route and the reverse route to/from at least any one of the input shaft and the output shaft.

TECHNICAL FIELD

The present invention relates generally to a transmission unit fortransmitting power of a prime mover of an automobile, and moreparticularly, to a power transmission unit comprising a transmissionroute including a continuously variable transmission, and anothertransmission route arranged parallel to said transmission route.

BACKGROUND ART

Generally, an output torque of an internal combustion engine isincreased with an increase in a rotational speed, but a vehicle requiresa large drive force at low speed and small drive force at high speed.That is, the vehicle required opposite torque characteristic to thatgenerated by the engine. In addition, optimum operating points of theengine are limited. Therefore, the vehicle having the engine as a primemover is provided with a transmission to alter a speed ratio accordingto need so that the engine is allowed to be operated at the optimumoperating points to generate drive force by altering the speed ratio ofthe transmission based on a running condition such as a vehicle speed,an accelerator opening etc. However, if a geared transmission adapted toshift a gear stage stepwise is used in the vehicle, the engine cannot bealways operated at optimum operating points. That is, if the optimumoperating speed exists between the gear stages, the operating efficiencyof the engine would be worsened. In order to avoid such disadvantage, acontinuously variable transmission has been used in place of the gearedtransmission.

A belt-driven continuously variable transmission and a toroidalcontinuously variable transmission are commonly used in vehicles. Thebelt driven continuously variable transmission is comprised of a beltfor transmitting power a pair of pulleys and a belt running on thosepulleys to transmit power therebetween. A speed ratio of between thosepulleys is altered continuously by changing a groove width of thepulleys to vary a running radius of the belt. In turn, the toroidalcontinuously variable transmission is comprised of a pair of discs beingopposed to each other, and a power roller interposed between thosediscs. Rotational speeds of those discs are differentiated depending onan inclination of a line connecting contact points between the powerroller and each discs with respect to a rotational center of the powerroller. That is, speed difference between the disc, i.e., a speed ratiois changed from “1” with an increment in the inclined angle (or tiltingangle) of the power roller.

The continuously variable transmission of those kinds are adapted totransmit torque utilizing a friction between the pulley and the belt ora friction between the disc and the power roller so that a speed ratiothereof can be altered continuously. Since the friction is a product ofa friction coefficient and a vertical load (or a loading in a normaldirection) at the contact points of two members, the larger verticalload is required with an increase in the torque to be transmitted.Specifically, in the belt driven continuously variable transmission ofvehicle the vertical load is a load of the pulley to clamp the belt. Tothis end, the required load is established by delivering hydraulic fluidto a hydraulic actuator integrated with the pulley.

A large drive force is required to launch the vehicle, but a requireddrive force to cruise the vehicle is smaller than that to launch thevehicle. That is, the larger vertical load is required to establish thefriction to launch the vehicle. Specifically, in the belt-drivencontinuously variable transmission, higher hydraulic pressure to clampthe belt is required when launching the vehicle. In order to launch thevehicle promptly, an additional hydraulic device for establishing largerhydraulic pressure is required. Consequently, the larger drive systemand the hydraulic system will be enlarged by such additional hydraulicdevice. In addition, fuel economy will be worsened as a result ofestablishing high pressure.

Japanese Patent Laid-Opens Nos. 2000-130548, 2004-076876, 2005-308041describe systems for dealing with the foregoing disadvantages. JapanesePatent Laid-Open No. 2000-130548 describes a system for a vehiclecomprised of a gear train connected to an input shaft through a firstclutch, and a continuously variable transmission connected to the inputshaft through a second clutch. The gear train is configured to establishforward speed stages and a reverse speed stage. A torque is transmittedfrom a drive gear disposed on an input shaft to a first countershaft,and further transmitted from the first countershaft selectively to aforward gear train and reverse gear train.

A driven gear meshing with the drive gear and a reverse drive gear arefitted onto the first countershaft. An output drive gear and a reversedriven gear are arranged coaxially while being allowed to rotate. A dogclutch is individually disposed between the first countershaft and theoutput drive gear, and between the output drive gear and the reversedriven gear. The first countershaft is connected to the output drivegear through the dog clutch, or the reverse driven gear is connected tothe output drive gear through the dog clutch. A first idle gear isfitted onto a first idler shaft to be meshed with the reverse drivengear disposed on the first countershaft. A second idle gear is disposedon the idler shaft to be meshed with the first idle gear. A third idlegear is disposed on the second idler shaft to be meshed with the reversedriven gear.

The output drive gear is meshed with an output driven gear fitted ontoan output shaft while being allowed to rotate. A one-way clutch and athird clutch juxtaposed in parallel each other are disposed between theoutput drive gear and an output shaft. A secondary pulley of driven sideis fitted onto the output shaft of the belt driven continuously variabletransmission, and a primary pulley of drive side is fitted onto theinput shaft. Those primary and secondary pulleys are connected through abelt running thereon. The input shaft and the primary pulley areconnected through the second clutch.

According to the Japanese Patent Laid-Open No. 2000-130548, the vehicleis launched in forward direction by engaging the first clutch whileconnecting the first countershaft to the output drive gear through thedog clutch thereby transmitting torque from the input shaft to theoutput shaft through the gear train. By contrast, the torque istransmitted from the input shaft to the reverse driven gear and theoutput drive gear through the first countershaft, the first idler shaft,and the second idler shaft, by engaging the first clutch whileconnecting the reverse driven gear to the output drive gear through thedog clutch. Consequently, the output shat is rotated in a directionopposite to the direction to propel the vehicle in the forwarddirection, that is, a reverse stage is established. In addition, thetorque is transmitted from the input shaft to output shaft trough thebelt-driven continuously variable transmission by engaging the secondclutch instead of the first clutch to propel the vehicle in a forwarddirection while alerting a speed ratio continuously.

Japanese Patent Laid-Open No. 2004-076876 describes a power transmissiondevice in which a torque reversing device comprised of a single pinionplanetary gear unit is disposed between an input shaft transmittingpower from an engine and a primary pulley of a belt-driven continuouslyvariable transmission. A ring gear of the torque reversing device isconnected with the primary pulley to be rotated therewith, and a sungear is connected with an input shaft. Therefore, a forward stage isachieves by connecting the sun gear with the ring gear by a clutch, anda reverse stage is achieved by fixing a carrier by a brake. In addition,a gear train adapted to establish a speed ratio a larger than a maximumspeed ratio of a continuously variable transmission is formed betweenthe input shaft and the output shaft integrated with a secondary pulley.An input gear of the gear train is integrated with the input shaft, andan output gear connected with the input shaft through an idle gear isfitted onto the output shaft while being allowed to rotate. In addition,a one-way clutch and a friction clutch are arranged in series betweenthe output gear and the output shaft.

Accordingly, when launching the vehicle in the forward direction, theclutch for connecting the input shaft with the primary pulley isdisengaged while engaging the clutch of the output shaft side, therebytransmitting torque to the output shaft from the input shaft through thegear train, the one-way clutch, and the clutch arranged in seriestherewith. The maximum speed ratio of the continuously variabletransmission is slightly smaller than that of the gear train. In thissituation, therefore, the secondary pulley and the output shaftintegrated therewith are rotated at a speed higher than the previousspeed and a rotational speed of output gear so that the one-way clutchis brought into disengagement. Consequently, the torque is transmittedto the output shaft through the continuously variable transmission.Since the gear train thus transmits the torque when launching thevehicle, a large torque is not applied to the continuously variabletransmission when launching the vehicle.

According to the teachings of Japanese Patent Laid-Open No. 2005-308041,an engine power is applied to a sun gear of a single-pinion planetarygear unit serving as a torque reversing device, and the sun gear isconnected to an input shaft integrated with a primary pulley of abelt-driven continuously variable transmission through a clutch. Aninput gear is fitted onto the input shaft through a one-way clutch, andthe input gear is connected with a ring gear of torque reversing device.The one-way clutch is adapted to be engaged when the input shaft rotatesin a forward direction at higher speed than the input gear situated atthe outer circumferential side. An output gear is fitted onto an outputshaft integrated with a secondary pulley through another one-way clutch,and an idle gear is disposed between the output gear and the input gearwhile being meshed therewith. That is, the input gear and the outputgear are rotated together in the same direction. A gear ratio (or speedratio) between the input gear and the output gear is slightly smallerthan the maximum speed ratio of the continuously variable transmissioncomprised of those pulleys and the belt wrapped around those pulleys.Said another one-way clutch is adapted to be engaged when the outputshaft rotates in the forward direction at higher speed than the outputgear. In addition, a friction clutch is arranged in parallel with saidone-way clutch. Further, a brake to fix a carrier of the torquereversing device is arranged to drive the vehicle in the backwarddirection.

Thus, in the power transmission device taught by Japanese PatentLaid-Open No. 2005-308041, the vehicle is launched in the forwarddirection by connecting the sun gear with the input shaft by the clutchto transmit the torque to main speed change route comprised of thecontinuously variable transmission the through the input shaft, and byengaging the one-way clutch to further transmit the torque to a subspeed change route. In this situation, since the speed ratio of the geartrain is slightly smaller than the maximum speed ratio of thecontinuously variable transmission, the output gear rotates at higherspeed than the output shaft. Consequently, the one-way clutch at theoutput shaft side is brought into disengagement so that the torque istransmitted to the drive wheels through the gear train. Therefore, thelarge torque will not be applied to the continuously variabletransmission when launching the vehicle. After launching the vehicle,the speed ratio of the continuously variable transmission is graduallyreduced with an increase in the vehicle speed so that a rotational speedof the output shaft integrated with the secondary pulley is raised tothat of the output gear situated outer circumferential side of theoutput shaft, and then further raised with a decrease in the speedratio. As a result, the one-way clutch of output shaft side is broughtinto engagement so that the torque is transmitted to the drive wheelsthrough the continuously variable transmission. In this situation, theone-way clutch of the input shaft side is in disengagement, therefore aninterlock will not occur.

In any of the teachings of those prior art documents, the gear train isarranged in parallel with the belt-driven continuously variabletransmission, and the torque for propelling the vehicle is transmittedthrough the gear train. Especially, according to Japanese PatentLaid-Open No. 2000-130548, the torque applied to the gear train isselectively transmitted through the dog clutch to the gear train forlaunching the vehicle and to the gear train for propelling the vehiclein the backward direction. To this end, in the continuously variabletransmission taught by Japanese Patent Laid-Open No. 2000-130548 a totalof four engagement elements is required such as the first clutch, thesecond clutch, the dog clutch, and the one-way clutch. In addition, thethird clutch arranged in parallel with the one-way clutch is alsorequired. According to the teachings of Japanese Patent Laid-Open No.2000-130548, therefore, the torque can be transmitted to launch thevehicle and to propel the vehicle in the backward direction withoutusing the belt-driven continuously variable transmission. However, largenumber of engagement elements is required to establish such torquetransmission route. Therefore, the structure of the transmission iscomplicated and dimension thereof is enlarged.

As described, according to the teachings of Japanese Patent Laid-OpenNo. 2000-130548, the torque transmission route for propelling thevehicle in the forward direction and the torque transmission route forpropelling the vehicle in the backward direction are switched by the dogclutch. Therefore, a shifting delay may occur during the so-calledgarage shifting. That is, the dog clutch is switched without applyingthe torque thereto. According to the teachings of Japanese PatentLaid-Open No. 2000-130548, therefore, a torque transmission to the dogclutch has to be cut off by disengaging the first clutch, and in thissituation, the dog clutch is switched and then the first clutch isengaged. Therefore, it takes time to wait the torque applied to the dogclutch disappears, and the first clutch is engaged after conforming afact that the dog clutch is switched. Thus, according to the teachingsof Japanese Patent Laid-Open No. 2000-130548, the switching operation ofthe dog clutch and the engaging operation of the first clutch may bedelayed inevitably to deteriorate shifting response during the garageshifting.

According to the teachings of Japanese Patent Laid-Open No. 2004-076876,the torque reversing mechanism establishes reverse stage when propellingthe vehicle in the backward direction. The torque transmitted throughthe torque reversing mechanism is transmitted to the belt-drivencontinuously variable transmission, and the torque is furthertransmitted to the drive wheels. According to the teachings of JapanesePatent Laid-Open No. 2004-076876, therefore, the speed ratio under thereverse stage may be restricted to the ratio possible to be achieved bythe continuously variable transmission.

The power transmission device taught by Japanese Patent Laid-Open No.2005-308041 is adapted to reduce the torque applied to the belt-drivencontinuously variable transmission when propelling the vehicle in theforward direction. Therefore, the speed ratio of the gear traintransmitting the torque when launching the vehicle is smaller than themaximum speed ratio that is possible to be achieved by the continuouslyvariable transmission. For this reason, a total range of the speed ratiocannot be widened.

DISCLOSURE OF THE INVENTION

The present invention has been conceived noting the foregoing technicalproblem, and it is therefore an object of the present invention is toprovide a power transmission unit for a vehicle in which a torquetransmission route can be selected from a plurality of transmissionroutes, and to simplify a structure of the power transmission unit whileimproving a speed change response.

The present invention is applied to a power transmission unit for avehicle comprised of: a continuously variable transmission that isadapted to alter a speed ratio continuously, and that is disposedbetween an input shaft to which a torque of a prime mover is inputtedand an output shaft that outputs the torque; a first gear train thattransmits the torque when propelling the vehicle in the forwarddirection; and a second gear train that transmits the torque whenpropelling the vehicle in the backward direction and that is arrangedparallel to the first gear train. In order to achieve theabove-explained objectives, the power transmission unit is providedwith: a first clutch device that selectively allows a torquetransmitting route from the input shaft to the output shaft via thefirst gear train to transmit the torque therethrough; a dog clutch thatswitches the torque transmitting route from the input shaft to theoutput shaft between a continuously variable speed change route in whichthe torque is transmitted through the continuously variable transmissionand a reverse route in which the torque is transmitted through thesecond gear train; a second clutch device that selectively enables anddisables both of the continuously variable speed change route and thereverse route to transmit the torque to the input shaft or the outputshaft; and a counter gear pair that is disposed at a site to transmitthe torque of the input shaft to the continuously variable transmissionroute and to the reverse route, and that is involved in a torquetransmission between the input shaft and the continuously variabletransmission route and a torque transmission between the input shaft andthe reverse route.

The first gear train is adapted to establish a speed ratio larger than amaximum speed ratio of the continuously variable transmission or a speedratio smaller than a minimum speed ratio of the continuously variabletransmission using a plurality of gears.

A movable member of the dog clutch is engaged with an input member forthe continuously variable speed change route and the reverse route, orwith an output member for the reverse route. The dog clutch thusstructured is adapted to enable a torque transmission through thecontinuously variable speed change route by engaging the movable memberwith a member forming a part of the continuously variable speed changeroute, and to enable a torque transmission through the reverse route byengaging the movable member with a member forming a part of the reverseroute.

The first clutch device and the second clutch device are individuallyformed by a single clutch.

Specifically, the first clutch device and the second clutch device maybe individually formed by a fiction clutch.

For example, the dog clutch may be disposed at a site to transmit thetorque to the output shaft while switching the torque transmission routebetween the continuously variable speed change route and the reverseroute. In this case, the counter gear pair is allowed to use the drivegear arranged coaxially with the input shaft commonly to transmit torquebetween the input shaft and the continuously variable speed changeroute, and to transmit torque between the input shaft and the reverseroute.

The first clutch device is disposed between the input shaft and thefirst gear train, and the first gear train is connected to the outputshaft.

Alternatively, the first clutch device disposed between the output shaftand the first gear train may also be connected to the input shaft.

The second clutch device may be disposed at a site to transmit thetorque of the input shaft to the continuously variable speed changeroute and to the reverse route.

Alternatively, the second clutch device may also disposed at a site totransmit the torque from the continuously variable speed change routeand the reverse route to the output shaft.

The dog clutch may also be disposed at a site to transmit the torque ofthe input shaft selectively to the continuously variable speed changeroute and to the reverse route.

According to the present invention, the torque transmission route fromthe input shaft to the output shaft is selected from the route passingthrough the first gear train, the route passing through the second geartrain, and the route passing through the continuously variabletransmission. In order to switch the torque transmission route, onlythree engagement devices such as the first clutch device, the secondclutch device and the dog clutch are employed. Thus, according to thepresent invention, the torque transmission route can be selected frommultiple options but number of the required engagement devices is rathersmall. Therefore, a structure of the power transmission unit can besimplified so that the power transmission unit can be downsized.According to the present invention, especially, the route fortransmitting torque through the continuously variable transmission andthe route for transmitting torque through the second gear train topropel the vehicle backwardly can be switched by the common dog clutch.Therefore, the structure of the power transmission unit can besimplified so that the power transmission unit can be downsized.

According to the present invention, the first gear train is adapted toestablish a speed ratio larger than the maximum speed ratio of thecontinuously variable transmission or a speed ratio smaller than theminimum speed ratio of the continuously variable transmission.Therefore, a possible range of the speed ratio of the power transmissionunit can be widened.

As described, according to the present invention, each clutch device isindividually formed of a single clutch. Therefore, the powertransmission unit can be further downsized. For example, a frictionclutch may be used as the clutch device. In this case, the torquetransmission route may be switched from the route through the first geartrain to the route through the continuously variable transmission or tothe route through the second gear train by the clutch-to-clutch shiftingwhile causing a slip of each friction clutch transitionally to switchthe clutch to transmit the torque. For this reason, a control responseof the shifting operation such as a garage shifting can be improved. Inaddition, shift shocks can be reduced.

In case of arranging the dog clutch in the output side, the drive gearmay be used commonly in the gear pair for transmitting torque from theinput shaft to the continuously variable speed change route, and in thegear pair for transmitting torque from the input shaft to the reverseroute. In other words, the counter gear pair or the gear train of thecontinuously variable speed change route and the counter gear pair orthe gear train of the reverse route are allowed to share the commongear. Therefore, the structure of the power transmission unit can befurther simplified so that the power transmission unit can be furtherdownsized.

Given that the clutch device and the dog clutch are arranged on theinput side, that is, at a site possible to transmit the torque from theinput shaft, the torque multiplied by a speed reduction will not beapplied to the clutch devices and the dog clutch. Therefore, the clutchdevices can be downsized and the torque capacity thereof can be reduced.

By contrast, if the clutch device and the dog clutch are arranged on theoutput side, that is, at a site possible to transmit the torque to theoutput shaft, a speed difference between an input side and an outputside of the clutch device or the dog clutch can be reduced so that theslip of the clutch device or the dog clutch can be reduced to improvedurability thereof. In addition, the input speed and the output speed ofthe dog clutch can be synchronized easily so that the dog clutch can beengaged or disengaged smoothly. Therefore, the dog clutch that does nothave a synchronizing member can be used instead of a synchronizer havinga synchronizing function so that the cost of the power transmission unitcan be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a skeleton diagram showing a first example of the powertransmission unit for a vehicle according to the present invention.

FIG. 2 is a skeleton diagram showing a structure of a dog clutch.

FIG. 3 is a table showing engagement states of the first clutch device,the second clutch device and the dog clutch.

FIG. 4 is a skeleton diagram showing a second example of the powertransmission unit for a vehicle according to the present invention.

FIG. 5 is a skeleton diagram showing a third example of the powertransmission unit for a vehicle according to the present invention.

FIG. 6 is a skeleton diagram showing a fourth example of the powertransmission unit for a vehicle according to the present invention.

FIG. 7 is a skeleton diagram showing a fifth example of the powertransmission unit for a vehicle according to the present invention.

FIG. 8 is a skeleton diagram showing a sixth example of the powertransmission unit for a vehicle according to the present invention.

FIG. 9 is a skeleton diagram showing a seventh example of the powertransmission unit for a vehicle according to the present invention.

FIG. 10 is a skeleton diagram showing an eighth example of the powertransmission unit for a vehicle according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

According to the present invention, there is provided a powertransmission unit for transmitting a power of a prime mover such as anengine and a motor, and the power transmission unit has a speed changefunction. In general, this kind of power transmission unit is called atransmission or a transaxle. More specifically, the present invention isapplied to a power transmission unit in which a continuously variabletransmission and a gear train of predetermined speed ratio (or a gearratio) are arranged parallel to each other between an input shaft and anoutput shaft. In the power transmission unit, a conventional belt-drivencontinuously variable transmission and a toroidal continuously variabletransmission may be used. Specifically, the belt-driven continuouslyvariable transmission is suitable for a power transmission unit of an FFlayout vehicle (i.e., a front engine/front wheel drive vehicle), and thetoroidal continuously variable transmission is suitable for a powertransmission unit of an FR layout vehicle (i.e., a front engine/rearwheel drive vehicle).

The gear train is formed to transmit a torque from an input shaft to anoutput shaft, and adapted to establish a speed ratio which cannot beestablished by the continuously variable transmission according to need.To this end, the gear train is formed by meshing a plurality of gears,and a gear ratio (i.e., a ratio between numbers of tooth) thereof isadjusted to establish a speed ratio larger than a maximum speed ratio ofthe continuously variable transmission or a speed ratio smaller than aminimum speed ratio of the continuously variable transmission. In orderto prevent the continuously variable transmission from being subjectedto a large torque for launching the vehicle, it is preferable to formthe gear train in a manner to establish a speed ratio larger than amaximum speed ratio of the continuously variable transmission. Bycontrast, in order to improve a fuel economy by lowering a speed of aprime mover, it is preferable to form the gear train in a manner toestablish a speed ratio smaller than a minimum speed ratio of thecontinuously variable transmission.

Referring now to FIG. 1, there is shown a first example of the powertransmission unit adapted for the FF layout vehicle. Accordingly, abelt-driven continuously variable transmission is employed as acontinuously variable transmission 1, and an internal combustion enginesuch as a gasoline engine is employed as a prime mover (as will becalled the “engine” hereinafter, and abbreviated as “Eng” in thedrawings) 2.

A conventional torque converter 3 having a lockup clutch 8 is connectedto an output shaft (i.e., a crank shaft) of the engine 2. The torqueconverter 3 is comprised of a pump impeller 5 integrated with a frontcover 4, a turbine runner 6 being opposed to the pump impeller 5, and astator 7 that is held through a not shown one-way clutch and that isinterposed between the pump impeller 5 and the turbine runner 6. Thelockup clutch 8 is arranged to be opposed to an inner face of the frontcover 4 in a manner to be rotated together with the turbine runner 6.Therefore, the lockup clutch 8 is engaged with the inner face of thefront cover 4 to transmit torque therebetween depending on a differencebetween pressures on both sides of the lockup clutch 8. Such torquetransmission between the lockup clutch 8 and the front cover 4 isinterrupted by disengaging the lockup clutch 8 from the inner face ofthe front cover 4. The turbine runner 6 is connected to an input shaft9.

A drive gear 10 for launching the vehicle is fitted onto the input shaft9 while being allowed to rotate, and a first clutch device C1 isarranged coaxially with the input shaft 9 to selectively connect thedrive gear 10 with the input shaft 9. In order to thus connect the drivegear 10 with the input shaft 9, a friction clutch, a dog clutch or aone-way clutch may be used as the first clutch device C1. According tothe first example shown in FIG. 1, any of a multiple plate type and asingle plate type, and a dry type or wet type friction clutch may beemployed as the first clutch device C1 so as to simplify a structure ofthe power transmission unit and to carry out an after-explainedclutch-to-clutch shifting. A reverse drive gear 11 is also fitted ontothe input shaft 9 in a manner to be rotated integrally therewith. Thus,according to the first example shown in FIG. 1, the foregoing elementsare arranged in order of the torque converter 2, the first clutch deviceC1, and the reverse drive gear 11.

A primary pulley (i.e., a drive pulley) of the continuously variabletransmission 12 is radially offset from the input shaft 9. A counterdriven gear 14 meshing with the reverse drive gear 11 is fitted onto theprimary shaft 13 rotated integrally with the primary pulley 12.Therefore, the primary shaft 13 is rotated in the direction opposite tothe rotational direction of the input shaft 9.

In order to deliver the torque to a front differential 16 as a finalreduction gear unit, an output shaft 15 is arranged parallel to theinput shaft 9. To this end, an output gear 18 meshing with a ring gear17 of the front differential 16 is fitted onto the output shaft 15 in amanner to be rotated integrally therewith. In addition, a driven gear 19for launching the vehicle meshing with the drive gear 10 is also fittedonto the output shaft 15 in a manner to be rotated integrally therewith.That is, the torque is delivered from the input shaft 9 to the outputshaft 15 through the first clutch device C1, the drive gear 10 and thedriven gear 19. Thus, the drive gear 10 and the driven gear 19 form thefirst gear train of the invention serving as a starting transmissionmechanism for launching the vehicle in the forward direction.Specifically, a gear ratio (or a speed ratio) between the drive gear 10and the driven gear 19 is adjusted to establish a speed ratio (of thelow speed side) larger than a maximum available speed ratio (i.e., aspeed ratio of the lowest speed side) of the continuously variabletransmission 1.

An intermediate shaft 20 is arranged coaxially with the output shaft 15,and a second clutch device C2 is disposed between the output shaft 15and the intermediate shaft 20, that is, at a site to transmit a torqueto the output shaft 15. In order to selectively connect the output shaft15 and the intermediate shaft 20, as the first clutch device C1, afriction clutch, a dog clutch, or a one-way clutch may be used as thesecond clutch device C2. According to the first example shown in FIG. 1,any of a multiple plate type and a single plate type, and a dry type andwet type friction clutches may be used as the second clutch device C2 soas to simplify a structure of the power transmission unit and to carryout an after-explained clutch-to-clutch shifting.

A reverse transmission mechanism is interposed between the intermediateshaft 20 and the input shaft 9. The above-explained startingtransmission mechanism formed by the drive gear 10 and the driven gear19 is adapted to transmit the torque in a manner to rotate the outputshaft 15 in an opposite direction to a rotational direction of the inputshaft 9 when transmitting the torque from the input shaft 9 to theoutput shaft 15. By contrast, the reverse transmission mechanism isadapted to transmit the torque in a manner to rotate the intermediateshaft 20 in the same direction as the rotational direction of the inputshaft 9 when transmitting the torque from the input shaft 9 to theintermediate shaft 20. To this end, an idle gear 21 is interposedbetween the input shaft 9 and the intermediate shaft 20 in a manner torotate around an axial line parallel to those shafts 9 and 20.Specifically, the idle gear 19 is meshed with the reverse drive gear 11disposed on the input shaft 9 while being meshed with a reverse drivengear 22 fitted onto the intermediate shaft 20 in a rotatable manner.Accordingly, the reverse drive gear 11, the idle gear 21, and thereverse driven gear 22 serve as the second gear train of the invention,and a route for transmitting the torque to the output shaft 15 throughthe reverse gear 11, the idle gear 21 and the reverse driven gear 22serves as the reverse route of the invention. In addition, the reversedrive gear 11 and the idle gear 21 form the counter gear pair of theinvention that is involved in a torque transmission between the inputshaft 9 and the reverse route.

A dog clutch 23 is arranged to selectively connect and disconnect thereverse driven gear 22 to/from the intermediate shaft 20. The dog clutch23 is adapted to be brought into engagement and disengagement but is notadapted to be brought into partial engagement while causing a slip. Forexample, a clutch engaged through a spline may be used as the dog clutch23, and an example thereof is schematically shown in FIG. 2. As shown inFIG. 2, a hub 24 is formed on the intermediate shaft 20 and a hub 25 isformed on the reverse driven gear 22, and a spline is formedindividually on an outer surface of each hub 24, 25. Those hubs 24 and25 are arranged close to each other, and a sleeve 26 is splined ontothose hubs 24 and 25 while being allowed to reciprocate in an axialdirection. Therefore, the intermediate shaft 20 is disconnected from thereverse driven gear 22 by moving the sleeve 26 to a position where thesleeve 26 is disengaged from any of the hubs 24 and 25. By contrast, theintermediate shaft 20 is connected with the reverse driven gear 22 totransmit the torque therebetween by moving the sleeve 26 to a positionwhere the sleeve 26 is engaged with both hubs 24 and 25. To this end, anot shown actuator is employed to reciprocate the sleeve 26 in the axialdirection.

As known in the prior art, the continuously variable transmission 1 iscomprised of the primary pulley 12 as a drive member, a secondary pulley27 as a driven member, and a belt 28 running on those pulleys 12 and 27.Accordingly, a speed ratio of the continuously variable transmission 1can be changed continuously by widening or narrowing groove widths ofthe pulleys 12 and 27 thereby altering running radii of the belt 28.

As described, the primary pulley 12 is radially offset from the inputshaft 9. In addition, the primary shaft 13 integrated with the primarypulley 12 is connected to the input shaft 9 to transmit power theretothrough the reverse drive gear 11 fitted onto the input shaft 9, and thecounter driven gear 14 fitted onto the primary shaft 13 while beingmeshed with the reverse drive gear 11. Accordingly, the reverse drivegear 11 and the counter driven gear 14 form the counter gear pair of theinvention that is involved in a torque transmission between the inputshaft 9 and the continuously variable transmission route.

On the other hand, the secondary pulley 27 is disposed in a manner torotate around a rotational axis parallel to a rotational axis of theprimary pulley 12, and provided with a secondary shaft 29 extendingalong with the rotational axis thereof. Specifically, the secondaryshaft 29 extends coaxially with the output shaft 15 and the intermediateshaft 20.

A hub 30 similar to the above-mentioned hubs 24 and 25 of the dog clutch23 is formed on a leading end of the secondary shaft 29 to be opposed tothe intermediate shaft 20. Therefore, the secondary shaft 29 isconnected selectively with the intermediate shaft 20 by theabove-explained dog clutch 23. Specifically, the secondary shaft 29 isconnected with the intermediate shaft 20 to transmit the torquetherebetween by moving the sleeve 26 to a position where the sleeve 26is engaged with both hub 24 of the intermediate shaft 20 and the hub 30of the secondary shaft 29. By contrast, the secondary shaft 29 isdisconnected from the intermediate shaft 20 by moving the sleeve 26 to aposition where the sleeve 26 is disengaged from any of the hubs 24 and30.

As shown in FIG. 2, the hub 24 of the intermediate shaft 20 is situatedin the middle, and the hub 30 of the secondary shaft 29 and the hub 25of the reverse driven gear 22 are situated on both sides of the hub 24.Therefore, the dog clutch 23 can be brought into a neutral state bymoving the sleeve 26 to a position to be engaged only with the hub 24 ofthe intermediate shaft 20 without being engaged with the hubs 25 and 30.

Thus, a torque transmission route from the input shaft 9 to the hub 30through the continuously variable transmission 1 serves as thecontinuously variable transmission route of the invention. In theexample shown in FIG. 1, the sleeve 26 serves as the “movable member” ofthe invention, the hub 24 serves as the “input member” or the “outputmember” of the invention, the hub 25 serves as the “member forming apart of the reverse route” of the invention, and the hub 30 serves asthe “member forming a part of the continuously variable transmissionroute” of the invention. In the example shown in FIG. 1, accordingly,the dog clutch 23 is disposed at a site possible to transmit the torquefrom the continuously variable speed change route and the reverse routeto the output shaft 15.

A gear ratio between the reverse drive gear 11 and the counter drivengear 14 on the continuously variable speed change route may be set notonly to a ratio not to achieve a speed increasing or decreasing action,but also to a ratio to achieve a speed increasing or decreasing action.Given that the gear ratio between the reverse drive gear 11 and thecounter driven gear 14 is set to the ratio to achieve a speed increasingor decreasing action, a gear ratio between the drive gear 10 and thedriven gear 19 serving as the starting transmission mechanism is set toa ratio larger than a ratio achieved by the gear ratio between thereverse drive gear 11 and the counter driven gear 14 and the maximumspeed ratio of the continuously variable transmission 1.

In the power transmission unit of the present invention, when launchingthe vehicle in any of the forward and the backward direction, torque istransmitted to the output shaft 15 through the starting transmissionmechanism or the reverse transmission mechanism arranged parallel to thecontinuously variable transmission 1. Given that the speed of thevehicle running in the forward direction is increased to a certainextent, the torque is transmitted from the input shaft 9 to the outputshaft 15 through the transmission route having the continuously variabletransmission 1. For example, if a drive position (or a drive range) isselected by a not shown shifting device, the first clutch device C1 isengaged and the second clutch device C2 is disengaged. In this case, ifthe vehicle is stopping or running at a speed lower than a predeterminedspeed, the dog clutch 23 is actuated to establish a reverse stage.Specifically, the sleeve 26 is moved to the right side in FIGS. 1 and 2to connect the reverse driven gear 22 to the intermediate shaft 20.

The engagement states of the first clutch device C1, the second clutchdevice C2 and the dog clutch 23 are shown in FIG. 3. In FIG. 3, “ON”represents an engagement of the clutch, and “OFF” represents adisengagement of the clutch. As to the dog clutch 23, “R” represents aposition for propelling the vehicle in the backward direction, and “F”represents a position for propelling the vehicle in the forwarddirection. Here, FIG. 3 shows the states of the clutches under bothsituations where the drive torque is transmitted through thecontinuously variable transmission 1, and where the vehicle is propelledin the backward direction.

When launching the vehicle in the forward direction, the torque of theengine 2 is delivered through the input shaft 9 and the first clutchdevice C1 to the drive gear 10, the reverse drive gear 11, and theprimary pulley 12 of the continuously variable transmission 1. In thissituation, the torque of the reverse drive gear 11 is transmitted to theintermediate shaft 20 through the idle gear 21, the reverse driven gear22 and the dog clutch 23. However, since the second clutch device C2 isin disengagement, the torque will not be transmitted from theintermediate shaft 20 to the output shaft 15. Meanwhile, in thecontinuously variable transmission 1, the torque is also transmittedfrom the primary pulley 12 to the secondary pulley 27 through the belt28. However, since the dog clutch 21 establishes the reverse stage sothat the continuously variable transmission 1 is disconnected from theintermediate shaft 20, the torque will not be transmitted from thecontinuously variable transmission 1 to the intermediate shaft 20 andthe output shaft 15. Consequently, the torque applied to the input shaft9 is transmitted from the drive gear 10 to the output shaft 15 throughthe driven gear 19 meshing with the drive gear 10, and the torque isfurther transmitted from the output shaft 15 to the differential 16through the output gear 18.

Accordingly, the speed ratio for launching the vehicle in the forwarddirection is governed by the gear ratio between the drive gear 10 andthe driven gear 19 serving as the starting transmission mechanism. Thespeed ratio thus achieved is larger than the maximum sped ratio of thecontinuously variable transmission 1. According to the powertransmission unit of the present invention, therefore, the drive forcefor launching the vehicle can be increased sufficiently. In addition,since the drive force is transmitted without passing through thecontinuously variable transmission 1, it is not necessary to increase atorque transmitting capacity of the continuously variable transmission1. That is, it is not necessary to increase a belt clamping pressure sothat the power loss will not be increased and durability of thecontinuously variable transmission will not be deteriorated.

When the vehicle speed is increased to the predetermined speed afterlaunching the vehicle, the drive torque delivered to the input shaft 9is delivered to the output shaft 15 through the continuously variabletransmission 1 instead of the starting transmission mechanism. Suchalteration of the torque transmission route is carried out by thefollowing procedures. First of all, the sleeve 26 of the dog clutch 23is moved leftward in FIGS. 1 and 2 to the position “F” for propellingthe vehicle in the forward direction thereby disconnecting the reversedriven gear 22 from the intermediate shaft 20 while connecting thesecondary shaft 29 of the continuously variable transmission 1 with theintermediate shaft 20. In this situation, since the second clutch deviceC2 is in disengagement so that the intermediate shaft 20 is disconnectedfrom the output shaft 15, the torque is not applied to the dog clutch23. Therefore, the sleeve 26 is allowed to move in the axial directionto be disengaged from the hub 25 of the reverse driven gear 22. In thissituation, the secondary pulley 27 of the continuously variabletransmission 1 is rotated by the torque transmitted from the engine 2but the torque is not applied to the intermediate shaft 20 being allowedto rotate freely. Therefore, the sleeve 26 is allowed to move toward thesecondary shaft 29 to be engaged with the hub 30.

After thus switching the engagement state of the dog clutch 23, thefirst clutch device C1 is brought into disengagement and the secondclutch device C2 is brought into engagement. In this situation, sincethe speed ratio established by the starting transmission mechanism isdifferentiated from the speed ratio established by the continuouslyvariable transmission 1, the engine speed is lowered as a result of thusswitching the clutch device engaged to transmit the torque. Therefore,in case of engaging the first clutch device C1 while disengaging thesecond clutch device C2, those clutch devices C1 and C2 aretransitionally caused to slip. Specifically, an engagement pressure ofthe second clutch device C2 is increased gradually thereby increasingthe torque transmitting capacity thereof gradually, while reducing anengagement pressure of the first clutch device C1 thereby reducing thetorque transmitting capacity thereof gradually. That is, a conventionalclutch-to-clutch shifting is carried out to change the torque of theoutput shaft 15 smoothly thereby reducing shift shocks and uncomfortablefeeling.

In order to propel the vehicle in the backward direction, as shown inFIG. 3, the first clutch device C1 is brought into disengagement, thesecond clutch device C2 is brought into engagement, and the dog clutch23 is moved to the position “R” for propelling the vehicle in thebackward direction. In this case, therefore, the torque is nottransmitted from the input shaft 9 to the drive gear 10, and thestarting transmission mechanism do not transmit the drive torque. Inaddition, since the continuously variable transmission 1 is disconnectedfrom the intermediate shaft 20 and the output shaft 15 by thus movingthe dog clutch 23 to the position “R” for establishing the reversestage, the drive torque will not be transmitted to the output shaft 15through the continuously variable transmission 1. That is, under thereverse stage, the torque of the input shaft 9 is transmitted to theintermediate shaft 20 through the reverse drive gear 11, the idle gear21, the reverse driven gear 22 and the dog clutch 23. In this situation,since the second clutch device C2 is in engagement, the drive torque istransmitted from the intermediate shaft 20 to the output shaft 15 andfurther transmitted to the differential 16 through the output gear 18.Thus, since the reverse transmission mechanism is comprised of the idlegear 21, the input shaft 9 and the output shaft 15 are rotated in thesame direction opposite to the rotational direction of the output shaft15 of the case in which the torque is transmitted through the startingtransmission mechanism and the continuously variable transmission 1.Consequently, the vehicle is allowed to be propelled in the backwarddirection.

The engagement states of the first clutch C1, the second clutch C2 andthe dog clutch 23 for the case of launching the vehicle in the forwarddirection will be compared with the engagement states of the thoseclutches for the case of propelling the vehicle in the backwarddirection. In case of launching the vehicle in the forward direction,the dog clutch 23 is allowed to be moved to the position “R” forestablishing the reverse stage. That is, only the engagement states ofthe first clutch device C1 and the second clutch device C2 are differentbetween the case of launching the vehicle in the forward direction andthe case of propelling the vehicle in the backward direction. Therefore,the power transmission unit is allowed to carry out the clutch-to-clutchshifting under the garage shifting where the vehicle is propelled in theforward and the backward directions alternately, so as to engage anddisengage the first clutch device C1 and the second clutch device C2alternately. Thus, the shifting operation can be completed withoutshifting the engagement state of the dog clutch 23 so that the shiftingdelay can be reduced and the control response can be improved. Inaddition, in the power transmission unit shown in FIG. 1, only the threeengagement devices such as the first clutch device C1, the second clutchdevice C2 and the dog clutch 23 are involved in the torque transmissionand the torque interrupting. Therefore, a structure of the powertransmission unit can be simplified so that the power transmission unitcan be downsized.

Especially, according to the first example shown in FIG. 1, the torqueis transmitted from the first clutch device C1 to the output shaft 15through the drive gear 10 and the driven gear 19 serving as the startingtransmission mechanism. Therefore, the torque before multiplied by thespeed reduction is applied to the first clutch device C1. That is, arequired torque transmitting capacity of the first clutch device C1 issmall so that the first clutch device C1 can be downsized and thedurability thereof can be improved. In addition, the second clutchdevice C2 is arranged coaxially with the output shaft 15. Therefore,when the vehicle speed reaches the predetermined speed and the secondclutch device C2 is brought into engagement, the speed ratio of thecontinuously variable transmission 1 is raised to the maximum ratio sothat a difference between an input speed and an output speed of secondclutch device C2 is reduced. For this reason, slippage of the secondclutch device C2 can be reduced so that the durability thereof can beimproved. Such advantage may also be achieved under the garage shifting.That is, a difference between the speed ratio for launching the vehicleand the speed ratio under the reverse stage is rather small. Therefore,even if the second clutch device C2 is engaged and disengaged repeatedlyunder the garage shifting, transient slip of the second clutch device C2can be reduced so that the durability thereof can be improved.

In addition, the speed ratios of the starting transmission mechanism andthe reverse transmission mechanism are not significantly different fromthe maximum speed ratio of the continuously variable transmission 1, andthe engagement state of the dog clutch 23 arranged coaxially with theoutput shaft 15 is switched while disengaging the second clutch deviceC2. Therefore, the dog clutch 23 is allowed to be engaged or disengagedunder the condition where a speed difference between the drive side andthe driven side thereof is small and the torque applied thereto issmall. That is, the rotational speed of the dive side and the rotationalspeed of the driven side can be synchronized easily with each other bymoving the sleeve 26 in the engagement direction. In other words, sincethe rotational speeds of both sides of the dog clutch 23 can besynchronized easily, an additional dog clutch serving as a synchronizercan be omitted so that the cost of the power transmission unit can bereduced. Further, the dog clutch 21 is used not only to establish thereverse stage by axially moving the sleeve 26 but also to allow thetorque transmission through the continuously variable transmission 1.That is, the common dog clutch 23 has two functions for establishing thereverse stage and for carrying out the continuously variable speedchange. Therefore, according to the power transmission unit of thepresent invention, number of parts can be reduced so that the structurethereof can be simplified and the power transmission unit itself can bedownsized.

Further, according to the example shown in FIG. 1, the reverse drivegear 21 is meshed not only with the counter driven gear 14 to transmittorque between the input shaft 9 and the primary shaft 13 of thecontinuously variable transmission 1, but also with the reverse drivengear 22 to transmit torque between the input shaft 9 and the reversetransmission mechanism. That is, the continuously variable transmissionroute and the reverse transmission route share a common element.Therefore, the structure of the power transmission unit can be furtherdownsized.

Here will be explained a second example of the power transmission unitaccording to the present invention. As described, the first clutchdevice C1 is adapted to selectively allow and interrupt the torquetransmission through the starting transmission mechanism, the secondclutch device C2 is adapted to selectively allow and interrupt thetorque transmission through the reverse transmission mechanism, and thedog clutch 23 is adapted to switch the torque transmission route betweenthe route through the continuously variable transmission 1 and the routethrough the reverse transmission mechanism. An arrangement of the firstclutch device C1, the second clutch device C2 and the dog clutch 23 maybe altered from that shown in FIG. 1 arbitrarily according to need whilemaintaining the above-explained functions.

According to the second example shown in FIG. 4, the second clutchdevice C2 and the dog clutch 23 are arranged coaxially with the inputshaft 9 in addition to the first clutch C1. Specifically, theintermediate shaft 20 and the counter shaft 31 are arranged in order onan extension of the input shaft 9. In order to reverse a direction ofthe torque transmitted to the continuously variable transmission 1, acounter drive gear 32 is fitted onto the counter shaft 31 to be rotatedintegrally therewith. The second clutch device C2 is disposed betweenthe input shaft 9 and the intermediate shaft 20, that is, at a site totransmit the torque of the input shaft 9 to the continuously variabletransmission route and to the reverse route. Therefore, the input shaft9 is connected to the intermediate shaft 20 by the second clutch deviceC2 in case of establishing the speed ratio for propelling the vehicle inthe forward direction by the continuously variable transmission 1, andin case of propelling the vehicle in the backward direction.

The reverse drive gear 11 is fitted onto the intermediate shaft 20, andthe dog clutch 23 is disposed to selectively connect the intermediateshaft 20 with the reverse drive gear 11 to transmit the torquetherebetween. Specifically, the dog clutch 23 is disposed on a leadingend of the intermediate shaft 20 (of the counter shaft 31 side), and ifthe intermediate shaft 20 is disconnected from the reverse drive gear11, the dog clutch 23 connects the intermediate shaft 20 with thecounter shaft 31 to transmit the torque therebetween. The structure ofthe dog clutch 23 is identical to that shown in FIG. 2. That is,according to the second example shown in FIG. 4, the dog clutch 23 isdisposed at a site to transmit the torque of the input shaft 9 to thecontinuously variable transmission route and to the reverse route.Accordingly, in the second example shown in FIG. 4, the hub 24 serves asthe “input member” of the invention.

According to the example shown in FIG. 4, the primary pulley 12 of thecontinuously variable transmission 1 is radially offset from the countershaft 31 or the input shaft 9. The counter driven gear 14 is fitted ontothe primary shaft 13 rotated integrally with the primary pulley 12, andthe counter drive gear 32 meshing with the counter driven gear 14 isfitted onto the counter shaft 31. Therefore, the primary shaft 13 isrotated in the direction opposite to the rotational direction of theinput shaft 9.

The secondary pulley 27 of the continuously variable transmission 1 isarranged coaxially with the output shaft 15, and the secondary shaft 29rotated integrally with the secondary pulley 27 is connected to theoutput shaft 15 to rotate integrally therewith. In addition, the reversedriven gear 22 and the driven gear 19 of the starting transmissionmechanism are fitted onto the secondary shaft 29 or the output shaft 15.The remaining structures are similar to those of the first example shownin FIG. 1. Therefore, common reference numerals are allotted to thecommon elements in FIG. 4 and detailed explanations for those commonelements are omitted.

According to the second example of the power transmission unit shown inFIG. 4, the launching stage for launching the vehicle with the speedratio larger than the maximum speed ratio of the continuously variabletransmission 1, the continuously variable speed change stage using thecontinuously variable transmission 1, and the reverse stage fortransmitting torque through the reverse transmission mechanism can beachieved by engaging and disengaging the first clutch device C1, thesecond clutch device C2 and the dog clutch 23 as shown in FIG. 3.Specifically, the input shaft 9 is connected to the output shaft 15through the drive gear 10 and the driven gear 19 serving as the startingtransmission mechanism, by engaging the first clutch device C1 whiledisengaging the second clutch device C2. Consequently, the speed ratiolarger than the maximum speed ratio of the continuously variabletransmission 1 is established to launch the vehicle by the drive forceachieved in accordance with such a large speed ratio. In this situation,even if the sleeve 26 is situated at the position “R” for establishingthe reverse stage, the second clutch device C2 is in disengagement sothat the torque will not be transmitted to the reverse transmissionmechanism from the input shaft 9. Therefore, an interlocking will notoccur. Rather, the gear stage can be shifted from the launching stagepromptly to the reverse stage by engaging the first clutch device C1 anddisengaging the second clutch device C2 while moving the sleeve 26 ofthe dog clutch 23 to the position “R” for establishing the reversestage. That is, shifting response under the garage shifting can beimproved.

In addition, when launching the vehicle, the gear stage can be shiftedpromptly from the launching stage where the speed ratio is large to thecontinuously variable speed change stage where the speed ratio is variedcontinuously by the continuously variable transmission 1, by carryingout the clutch-to-clutch shifting to disengage the first clutch deviceC1 and to engage the second clutch device C2, while moving the sleeve 26of the dog clutch 23 to the position “F” for propelling the vehicle inthe forward direction. In this case, the response delay can also beavoided.

The advantages of the first example shown in FIG. 1 may also be achievedby the second example shown in FIG. 4 thus structured. Especially,according to the second example shown in FIG. 4, the second clutchdevice C2 is disposed on the input shaft 9 side. Therefore, the torquemultiplied to be larger than the torque from the input shaft 9 will notbe applied to the second clutch device C2. For this reason, the secondclutch device C2 can be downsized and the torque capacity thereof can bereduced in comparison with the first example shown in FIG. 1. Likewise,when the vehicle is running, the torque is also applied to the dogclutch 23 from the input shaft 9 without being multiplied by the speedchange operation. Therefore, the dog clutch 23 can also be downsized andthe torque capacity thereof can also be reduced.

FIG. 5 shows the third example as a modification of the first exampleshown in FIG. 1 in which the second clutch device C2 and a counter gearpair are arranged on the input shaft 9 side, and in which othernecessary alterations are made. In other words, the third example is amodification of the second example shown in FIG. 4 in which the dogclutch 23 is disposed on the output shaft 15 side, and in which othernecessary alterations are made. In the third example, the reverse drivegear 11, the idle gear 21, and the reverse driven gear 22 forming thereverse transmission mechanism are interposed between the second clutchdevice C2 and the dog clutch 23. Therefore, the counter shaft 25 used inthe example shown in FIG. 4 is not arranged in the third example.Specifically, the reverse drive gear 11 is fitted onto the intermediateshaft 20 connected to the input shaft 9 by the second clutch device C2,and the counter driven gear 14 meshing with the reverse drive gear 11 isfitted onto the primary shaft 13 offset from the intermediate shaft 20.That is, according to the third example shown in FIG. 5, the reversedrive gear 11 also serves as the aforementioned counter drive gear 32 toreduce number of gears. In other words, the counter drive gear 32 alsoserves as the reverse drive gear 11.

The dog clutch 23 is disposed between the secondary shaft 29 and theoutput shaft 15 arranged coaxially with each other, and the reversedriven gear 22 connected with the reverse drive gear 11 through the idlegear 21 is fitted onto the output shaft 15 while being allowed torotate. The hub 24 is formed integrally on the output shaft 15, and thehub 30 of the secondary shaft 29 and the hub 25 of the reverse drivengear 22 are situated across the hub 24. The sleeve 26 is splined ontothose hubs 24, 25 and 30 while being allowed to move in the axialdirection. Therefore, the reverse driven gear 22 or the secondary shaft29 is selectively connected with the output shaft 15 by moving thesleeve 26 in the axial direction. The remaining structures are similarto those of the example shown in FIG. 4. Therefore, common referencenumerals are allotted to the common elements in FIG. 5, and detailedexplanations for those common elements are omitted.

According to the third example of the power transmission unit shown inFIG. 5, the launching stage for establishing a large drive force, thecontinuously variable speed change stage where the drive torque istransmitted through the continuously variable transmission 1, and thereverse stage where the drive torque is transmitted through the reversetransmission mechanism can be achieved by engaging and disengaging thefirst clutch device C1, the second clutch device C2 and the dog clutch21 as shown in FIG. 3. Specifically, in case of launching the vehicle inthe forward direction, the first clutch device C1 is engaged and thesecond clutch device C2 is disengaged. Consequently, the input shaft 9is connected to the output shaft 15 through the drive gear 10, the firstclutch device C1 and the driven gear 19 forming the startingtransmission mechanism, and the reverse transmission mechanism and thecontinuously variable transmission 1 are disconnected from the inputshaft 9. Therefore, the speed ratio larger than the maximum speed ratioof the continuously variable transmission 1 is established by thestarting transmission mechanism to launch the vehicle by the drive forceestablished in accordance with such a large speed ratio. In thissituation, the gear stage can be shifted from the launching stagepromptly to the reverse stage by disengaging the first clutch device C1and engaging the second clutch device C2 while moving the sleeve 24 ofthe dog clutch 21 to the position “R” for establishing the reversestage. Therefore, the shifting response under the garage shifting can beimproved.

In addition, when launching the vehicle, the gear stage can be shiftedpromptly from the launching stage where the speed ratio is large to thecontinuously variable speed change stage where the speed ratio is variedcontinuously by the continuously variable transmission 1, by carryingout the clutch-to-clutch shifting to disengage the first clutch deviceC1 and to engage the second clutch device C2, while moving the sleeve 26of the dog clutch 23 to the position “F” for propelling the vehicle inthe forward direction. In this case, the response delay can also beavoided.

The advantages of the examples shown in FIGS. 1 and 4 may also beachieved by the third example shown in FIG. 5 thus structured. Inaddition, according to the third example shown in FIG. 5, number ofgears can be reduced. Specifically, as the example shown in FIG. 1, thereverse drive gear 21 is meshed not only with the counter driven gear 14to transmit torque from the input shaft 9 to the primary shaft 13 of thecontinuously variable transmission 1 through the intermediate shaft 20,but also with the reverse driven gear 22 to transmit torque from theinput shaft 9 to the reverse transmission mechanism through theintermediate shaft 20. Therefore, the structure of the powertransmission unit can be simplified so that the power transmission unitcan be downsized.

According to the third example shown in FIG. 5, when the engagementstate of the sleeve 26 of the dog clutch 23 is switched, that is, whenthe sleeve 26 is moved axially to be engaged with the hub 30 of thesecondary shaft 29 or the hub 25 of the reverse driven gear 22 whilebeing disengaged from the other hub, a speed difference between theoutput shaft 15 and the secondary shaft 29 or the reverse driven gear 22can be reduced by increasing the speed ratio of the continuouslyvariable transmission 1 to the ratio close to the maximum ratio.Therefore, as the power transmission unit shown in FIG. 1, therotational speeds of both sides of the dog clutch 23 can be synchronizedeasily so that an expensive and complex member such as a synchronizercan be eliminated.

FIG. 6 shows the fourth example as a modification of the first exampleshown in FIG. 1 in which the dog clutch 23 and the counter gear pair arearranged on the input shaft 9 side, and in which other necessaryalterations are made. In other words, the fourth example is amodification of the second example shown in FIG. 4 in which the secondclutch device C2 is disposed on the output shaft 15 side, and in whichother necessary alterations are made. According to the example shown inFIG. 6, specifically, the reverse drive gear 11 is fitted onto the inputshaft 9 while being allowed to rotate, and the reverse driven gear 22connected with the reverse drive gear 11 through the idle gear 21 isfitted onto the secondary shaft 29 while being allowed to rotateintegrally therewith. The output shaft 15 is arranged coaxially with thesecondary shaft 29, and the second clutch device C2 is disposed betweenthe secondary shaft 29 and the output shaft 15.

The counter shaft 25 is arranged on an extension of the input shaft 9,and the counter drive gear 32 fitted onto the counter shaft 31 is meshedwith the counter driven gear 14 fitted onto the primary shaft 13. Thedog clutch 23 is disposed between the input shaft 9 and the countershaft 31. Specifically, the input shaft 9 is connected with the reversedrive gear 11 by moving the sleeve 26 rightward in FIG. 6 to be engagedwith both of the hub 24 of the input shaft 9 and the hub 25 of thereverse drive gear 11. By contrast, the input shaft 9 is connected withthe primary shaft 13 by moving the sleeve 26 leftward in FIG. 6 to beengaged with both of the hub 24 of the input shaft 9 and the hub 30 ofthe primary shaft 13. The remaining structures are similar to those ofthe examples shown in FIGS. 1 and 4. Therefore, common referencenumerals are allotted to the common elements in FIG. 6, and detailedexplanations for those common elements are omitted.

As described, the example shown in FIG. 6 is different from the examplesshown in FIGS. 1 and 4 in the positions of the second clutch device andC2 and the dog clutch 23, and in other alterations. Therefore, as theforegoing examples, the launching stage for establishing a large drivetorque for propelling the vehicle in the forward direction, thecontinuously variable speed change stage using the continuously variabletransmission 1, and the reverse stage can be achieved by engaging anddisengaging the first clutch device C1, the second clutch device C2 andthe dog clutch 23 as shown in FIG. 3.

Specifically, in case of launching the vehicle in the forward direction,the first clutch device C1 is engaged and the second clutch device C2 isdisengaged. Consequently, the input shaft 9 is connected with the outputshaft 15 through the drive gear 10, the first clutch device C1 and thedriven gear 19 forming the starting transmission mechanism, and thereverse transmission mechanism and the continuously variabletransmission 1 are disconnected from the input shaft 9 by the dog clutch23 or the second clutch device C2. Therefore, the speed ratio largerthan the maximum speed ratio of the continuously variable transmission 1is established by the starting transmission mechanism to launch thevehicle by the drive force established in accordance with such a largespeed ratio. In this situation, the gear stage can be shifted from thelaunching stage promptly to the reverse stage by disengaging the firstclutch device C1 and engaging the second clutch device C2 while movingthe sleeve 26 of the dog clutch 23 to the position “R” for establishingthe reverse stage. Therefore, the shifting response under the garageshifting can be improved.

In addition, when launching the vehicle, the gear stage can be shiftedpromptly from the launching stage where the speed ratio is large to thecontinuously variable speed change stage where the speed ratio is variedcontinuously by the continuously variable transmission 1, by carryingout the clutch-to-clutch shifting to disengage the first clutch deviceC1 and to engage the second clutch device C2, while moving the sleeve 26of the dog clutch 23 to the position “F” for propelling the vehicle inthe forward direction. In this case, therefore, the response delay canalso be avoided.

The advantages of the examples shown in FIGS. 1 and 4 may also beachieved by the fourth example shown in FIG. 6 thus structured. In theexample shown in FIG. 6, the engagement state of the second clutchdevice C2 is altered when shifting the gear stage from the launchingstage to the continuously variable speed change stage using thecontinuously variable transmission 1 or to the reverse stage. However, aspeed difference between the output shaft 15 and the secondary shaft 29or the reverse driven gear 22 is rather small at the point of shifting.Therefore, as the example shown in FIG. 1, a transient slip of thesecond clutch device C2 when altering the engagement state can bereduced so that the durability thereof can be improved.

FIG. 7 shows the fifth example as a modification of the first exampleshown in FIG. 1 in which the members disposed on the input shaft 9 sidein the example shown in FIG. 1 are disposed on the output shaft 15 side,and the members disposed on the output shaft 15 side are disposed on theinput shaft 9 side. In other words, the fifth example is a modificationof the second example shown in FIG. 4 in which the first clutch deviceC1 is arranged coaxially with the output shaft 15. Accordingly, thedrive gear 10 is fitted onto the input shaft 9 to be rotated integrallytherewith. The driven gear 19 is fitted onto the output shaft 15 whilebeing allowed to rotate, and the first clutch device C1 selectivelyconnects and disconnects the driven gear 19 to/from the output shaft 15.The remaining structures are similar to those of the examples shown inFIGS. 1 and 4. Therefore, common reference numerals are allotted to thecommon elements in FIG. 7, and detailed explanations for those commonelements are omitted.

In the power transmission unit shown in FIG. 7, the launching stage forestablishing a large drive torque, the continuously variable speedchange stage using the continuously variable transmission 1, and thereverse stage transmitting the drive torque through the reversetransmission mechanism can be achieved by engaging and disengaging thefirst clutch device C1, the second clutch device C2 and the dog clutch23 as shown in FIG. 3. The torque transmitting routes and the torquetransmitting conditions under those stages, and procedures forestablishing those stages are identical to those of the foregoingexamples, therefore, detailed explanations will be omitted. Theadvantages of the foregoing examples may also be achieved by the fourthexample shown in FIG. 7 thus structured. In the example shown in FIG. 7,the dog clutch 23 is thus arranged in the input shaft 9 side. Therefore,the advantage of the example shown in FIG. 7 is that the torquemultiplied as a result of speed change will not be applied to the dogclutch 23, as the examples shown in FIGS. 4 and 6. Therefore, the dogclutch 23 can also be downsized and the torque capacity thereof can alsobe reduced. In addition, since the second clutch device C2 is arrangedin the input shaft 9 side, the torque multiplied to be larger than thetorque from the input shaft 9 will not be applied to the second clutchdevice C2 as the examples shown in FIGS. 4 and 6. Therefore, the secondclutch device C2 can be downsized and the torque capacity thereof can bereduced.

FIG. 8 shows the sixth example as a modification of the fifth exampleshown in FIG. 7 in which the dog clutch 23 is disposed on the outputshaft 15 side or the secondary shaft 39 side, and in which othernecessary alterations are made. The remaining structures are similar tothose of the example shown in FIG. 7. Therefore, common referencenumerals are allotted to the common elements in FIG. 8, and detailedexplanations for those common elements are omitted.

According to the power transmission unit shown in FIG. 8, the launchingstage for propelling the vehicle in the forward direction, thecontinuously variable speed change stage using the continuously variabletransmission 1, and the reverse stage for transmitting the drive torquethrough the reverse transmission mechanism can also be achieved byengaging and disengaging the first clutch device C1, the second clutchdevice C2 and the dog clutch 23 as shown in FIG. 3. According to theexample shown in FIG. 8, although the torque multiplied as a result ofspeed change is applied to the dog clutch 23, a speed difference betweenboth sides of the dog clutch 23 can be reduced. Therefore, therotational speeds of both sides of the dog clutch 23 can be synchronizedeasily when engaging the dog clutch 23, as the examples shown in FIGS.1, 5 and 7. In addition, since the reverse drive gear 11 (or the counterdrive gear 32) is used for multiple purpose, number of parts of thepower transmission unit can be reduced. Therefore, the structure of thepower transmission unit can be simplified so that the power transmissionunit itself can be downsized. That is, as the examples shown in FIGS. 1and 5, the reverse drive gear 21 is meshed not only with the counterdriven gear 14 to transmit torque from the input shaft 9 to the primaryshaft 13 of the continuously variable transmission 1 through theintermediate shaft 20, but also with the reverse driven gear 22 totransmit torque from the input shaft 9 to the reverse transmissionmechanism through the intermediate shaft 20. Therefore, the structure ofthe power transmission unit can be simplified so that the powertransmission unit can be downsized.

According to the example shown in FIG. 8, the torque transmitting routesand the torque transmitting conditions under the above-mentioned stages,and procedures for establishing those stages are identical to those ofthe foregoing examples, therefore, detailed explanations will beomitted. The advantages of the foregoing examples may also be achievedby the sixth example shown in FIG. 8 thus structured.

FIG. 9 shows the seventh example as a modification of the first exampleshown in FIG. 1 in which the first clutch device C1 is disposed on theoutput shaft 15 side and the dog clutch 23 is disposed on the inputshaft 9 side or the primary pulley 12 side, and in which other necessaryalterations are made. In other words, the seventh example is amodification of the fourth example shown in FIG. 6 in which the firstclutch device C1 is disposed on the output shaft 15 side, or amodification of the fifth example shown in FIG. 7 in which the secondclutch device C2 is disposed on the output shaft 15 side. The remainingstructures are similar to those of the examples shown in FIGS. 1, 6 and7. Therefore, common reference numerals are allotted to the commonelements in FIG. 9, and detailed explanations for those common elementsare omitted.

According to the power transmission unit shown in FIG. 9, the launchingstage for propelling the vehicle in the forward direction, thecontinuously variable speed change stage using the continuously variabletransmission 1, and the reverse stage for transmitting the drive torquethrough the reverse transmission mechanism can also be achieved byengaging and disengaging the first clutch device C1, the second clutchdevice C2 and the dog clutch 23 as shown in FIG. 3. Also, the torquetransmitting routes and the torque transmitting conditions under thosestages, and procedures for establishing those stages are identical tothose of the foregoing examples, therefore, detailed explanations willbe omitted. Since the structure of the power transmission unit shown inFIG. 9 is similar to those of the examples 6 and 7, the advantages ofthe foregoing examples shown in FIGS. 6 and 7 may also be achieved bythe seventh example shown in FIG. 9.

FIG. 10 shows the eighth example as a modification of the first exampleshown in FIG. 1 in which the first clutch device C1 is disposed on theoutput shaft 15 side and the counter gear pair is disposed on the inputshaft 9 side or the primary pulley 12 side, and in which other necessaryalterations are made. In other words, the eighth example is amodification of the fifth example shown in FIG. 7 in which the firstclutch device C1 and the dog clutch 23 are disposed on the output shaft15 side, or a modification of the sixth example shown in FIG. 8 in whichthe second clutch device C2 is disposed on the output shaft 15 side. Theremaining structures are similar to those of the examples shown in FIGS.1, 7 and 8. Therefore, common reference numerals are allotted to thecommon elements in FIG. 10, and detailed explanations for those commonelements are omitted.

According to the power transmission unit shown in FIG. 10, the launchingstage for propelling the vehicle in the forward direction, thecontinuously variable speed change stage using the continuously variabletransmission 1, and the reverse stage for transmitting the drive torquethrough the reverse transmission mechanism can also be achieved byengaging and disengaging the first clutch device C1, the second clutchdevice C2 and the dog clutch 23 as shown in FIG. 3. Also, the torquetransmitting routes and the torque transmitting conditions under thosestages, and procedures for establishing those stages are identical tothose of the foregoing examples, therefore, detailed explanations willbe omitted. Since the structure of the power transmission unit shown inFIG. 10 is similar to those of the examples 6 and 7, the advantages ofthe foregoing examples shown in FIGS. 6 and 7 may also be achieved bythe eighth example shown in FIG. 10.

For example, since the reverse drive gear 11 (or the counter drive gear32) is used for multiple purpose, number of parts of the powertransmission unit can be reduced. Therefore, the structure of the powertransmission unit can be simplified so that the power transmission unititself can be downsized. That is, as the examples shown in FIGS. 1, 5and 8, the reverse drive gear 21 is meshed not only with the counterdriven gear 14 to transmit torque from the input shaft 9 to the primaryshaft 13 of the continuously variable transmission 1 through theintermediate shaft 20, but also with the reverse driven gear 22 totransmit torque from the input shaft 9 to the reverse transmissionmechanism through the intermediate shaft 20. Therefore, the structure ofthe power transmission unit can be simplified so that the powertransmission unit can be downsized.

Thus, in the power transmission unit of the present invention, thetorque transmission route from the input shaft 9 to the output shaft 15can be selected from: the route passing through the first gear traincomprised of the drive gear 10 and the driven gear 19 (i.e., thestarting transmission mechanism); the route passing through the secondgear train comprised of the reverse drive gear 11, the idle gear 21 andthe reverse driven gear 22 (i.e., the reverse transmission mechanism);and the route passing through the continuously variable transmission 1(i.e., the continuously variable speed change route). In order to switchthe torque transmission route, only three engagement devices such as thefirst clutch device C1, the second clutch device C2 and the dog clutch23 are employed. That is, although the torque transmission route can beselected from multiple options, number of the required engagementdevices is rather small. According to the present invention, therefore,a structure of the power transmission unit can be simplified so that thepower transmission unit can be downsized.

According to the power transmission unit of the present invention,especially, the route for transmitting torque through the continuouslyvariable speed change route and the route for transmitting torquethrough the reverse route to propel the vehicle backwardly can beswitched by the common dog clutch. Therefore, the structure of the powertransmission unit can be simplified so that the power transmission unitcan be downsized.

Moreover, according to the present invention, the starting transmissionmechanism is adapted to establish a speed ratio larger than the maximumspeed ratio of the continuously variable transmission 1 or a speed ratiosmaller than the minimum speed ratio of the continuously variabletransmission 1. Therefore, a possible range of the speed ratio of thepower transmission unit can be widened.

Further, according to the present invention, the first clutch device C1,the second clutch device C2 and the dog clutch 23 are individuallyformed of a single clutch. Therefore, the power transmission unit can befurther downsized. For example, a friction clutch may be used as thefirst clutch device C1, the second clutch device C2 and the dog clutch23. In this case, the clutch-to-clutch shifting can be carried out toimprove a control response of the shifting operation such as a garageshifting. In addition, shift shocks can be reduced.

As described, according to the present invention, the dog clutch 23 mayalso be disposed on the output shaft 15 side. In this case, the countergear pair for transmitting torque from the input shaft 9 to thecontinuously variable transmission route is allowed to share a commondrive gear with the counter gear pair for transmitting torque from theinput shaft 9 to the reverse route. To this end, specifically, thereverse drive gear 21 is meshed with the counter driven gear 14 totransmit torque between the input shaft 9 and the primary shaft 13 ofthe continuously variable transmission 1, as well as with the reversedriven gear 22 to transmit torque between the input shaft 9 and thereverse transmission mechanism. Thus, the gear train forming thecontinuously variable transmission route and the reverse route areallowed to share the common gear. Therefore, the structure of the powertransmission unit can be further simplified so that the powertransmission unit can be further downsized.

In the foregoing examples, the speed ratio of the first gear trainbetween the drive gear 10 and the driven gear 19 are increased to belarger than the maximum speed ratio of the continuously variabletransmission 1. That is, the present invention is applied to establish aspeed ratio which cannot be established by the continuously variabletransmission 1 using the gear train. Therefore, a speed ratio smallerthan the minimum speed ratio of the continuously variable transmission 1may also be established using the first gear train. In this case, whenthe vehicle is propelled by running the engine under the low loadcondition, the engine speed can be reduced to be lower than the speedreduced by continuously variable transmission 1. For this reason, thefuel economy can be further improved. In addition, the first gear trainmay also be adapted to establish a plurality of different ratios.

The invention claimed is:
 1. A power transmission unit for a vehicle,comprising: a continuously variable transmission that is adapted toalter a speed ratio continuously, and that is disposed between an inputshaft to which a torque of a prime mover is inputted and an output shaftthat outputs the torque; a first gear train that transmits the torquewhen propelling the vehicle in the forward direction; and a second geartrain that transmits the torque to propel the vehicle backwardly byrotating the output shaft in an opposite direction to a rotationaldirection of the input shaft when propelling the vehicle in the backwarddirection and that is arranged parallel to the first gear train; a firstclutch device that selectively allows a torque transmitting route fromthe input shaft to the output shaft via the first gear train to transmitthe torque therethrough; a dog clutch that switches the torquetransmitting route from the input shaft to the output shaft between acontinuously variable speed change route in which the torque istransmitted through the continuously variable transmission and a reverseroute in which the torque is transmitted through the second gear train;a second clutch device that selectively enables and disables both of thecontinuously variable speed change route and the reverse route totransmit the torque to the input shaft or the output shaft; and acounter gear pair that is disposed at a site to transmit the torque ofthe input shaft to the continuously variable transmission route and tothe reverse route, and that is involved in a torque transmission betweenthe input shaft and the continuously variable transmission route and atorque transmission between the input shaft and the reverse route. 2.The power transmission unit for a vehicle as claimed in claim 1, whereinthe first gear train is adapted to establish a speed ratio larger than amaximum speed ratio of the continuously variable transmission or a speedratio smaller than a minimum speed ratio of the continuously variabletransmission using a plurality of gears.
 3. The power transmission unitfor a vehicle as claimed in claim 1, wherein the dog clutch is adaptedto: enable a torque transmission through the continuously variable speedchange route by engaging a movable member that is engaged with an inputmember for the continuously variable speed change route and the reverseroute or with an output member for the reverse route, with a memberforming a part of the continuously variable speed change route, andenable a torque transmission through the reverse route by engaging themovable member with a member forming a part of the reverse route.
 4. Thepower transmission unit for a vehicle as claimed in claim 1, whereineach of the first clutch device and the second clutch device isindividually formed by a single clutch.
 5. The power transmission unitfor a vehicle as claimed in claim 1, wherein each of the first clutchdevice and the second clutch device is individually formed by a fictionclutch.
 6. The power transmission unit for a vehicle as claimed in claim1, wherein the dog clutch is disposed at a site to transmit the torqueto the output shaft while switching the torque transmission routebetween the continuously variable speed change route and the reverseroute; and wherein a drive gear of the counter gear pair is arrangedcoaxially with the input shaft so as to commonly serve as one of gearsof a gear pair transmitting torque between the input shaft and thecontinuously variable speed change route, and one of gears of anothergear pair transmitting torque between the input shaft and the reverseroute.
 7. The power transmission unit for a vehicle as claimed in claim1, wherein the first clutch device is disposed between the input shaftand the first gear train; and wherein the first gear train is connectedto the output shaft.
 8. The power transmission unit for a vehicle asclaimed in claim 1, wherein the first clutch device is disposed betweenthe output shaft and the first gear train; and wherein the first geartrain is connected to the input shaft.
 9. The power transmission unitfor a vehicle as claimed in claim 1, wherein the second clutch device isdisposed at a site to transmit the torque of the input shaft to thecontinuously variable speed change route and to the reverse route. 10.The power transmission unit for a vehicle as claimed in claim 1, whereinthe second clutch device is disposed at a site to transmit the torquefrom the continuously variable speed change route and the reverse routeto the output shaft.
 11. The power transmission unit for a vehicle asclaimed in claim 1, wherein the dog clutch is disposed at a site totransmit the torque of the input shaft selectively to the continuouslyvariable speed change route and to the reverse route.